The invention described herein relates generally to slapper detonators, and more particularly to method and apparatus for supplying electric power to slapper detonators.
The well-known slapper detonator, described by John R. Stroud in the Lawrence Livermore Laboratory document UCRL-77639 dated Feb. 27, 1976 and titled "A New Kind of Detonator--The Slapper", operates by exploding a thin metal foil that drives a film of dielectric material across a gap to impact on a high-density explosive. The thin conductive metal foil is explosively vaporized with an electric current pulse that must have exactly the right characteristics for the detonator to function. In many applications, the foil comprises part of a thin portion of a flat-conductor detonator circuit. This thin portion must be short enough so that its resistance is no more than a few milliohms, and its inductance adds no more than a few nanohenrys to the inductance of the whole detonator circuit.
Concurrently, the thin conductive foil must be the most resistive component of the thin portion of the flat-conductor detonator circuit. Although the optimal parameters of the electric current pulse required to fire any slapper detonator will depend upon the specific geometry and material composition of that detonator and its thin conductive foil, the electric pulse typically must have a peak amplitude of about 2 to 4 kiloamps and a duration of approximately a few tenths of a microsecond. The electric pulse must deliver its energy to the thin foil in a time that is appreciably less than the time that it would take for the vaporized foil to come to thermal equilibrium with its surroundings.
It would be advantageous if electric power could be discriminatively distributed to multiplicities of slapper detonators dispersed throughout explosive assemblies such as mass-produced munitions. This process of distribution would be of increased benefit if it could be carried out under a varied spectrum of adverse environmental conditions, such as at reduced or elevated temperatures, or at pressures ranging from vacuum to superatmospheric. It would clearly be convenient to transport electric power to each slapper detonator of a detonator multiplicity via its own individual thick flat-conductor power cable, with the requisite multiplicity of power cables all coming from a single pulse generator. These coordinated groupings of power cables could advantageously be individually tailored for electric power pulse timing. Power cables suitable for this usage would have low inductance and resistance, typically only a few tens of both nanohenrys and milliohms. This potentially beneficial process of power distribution would require the transfer of temporally short electric power pulses from thick flat-conductor power cables into thin flat-conductor slapper detonator circuits. There are two known means for doing this.
One of these known means requires the power cables to be attached to the detonator circuits with electrical connectors. Unfortunately, the presently existing electrical connectors that can be used for this purpose are expensive and very complicated because of the wide array of different environments within which they must potentially function. These connectors tend to be bulky and heavy, have multiple seals, require soldering, and are very labor-intensive to work with. This last factor is especially disadvantageous if the connectors must be subject to integrity verification over extended and appreciable periods of time. Thus, while this methodology is potentially available for use, it is clearly beset with many detrimental conditions and inconveniences.
The other known solution to the short electric power pulse transfer problem involves permanently attaching the power cables to the detonator circuits in integrated assemblies. The two conductors that form the end of each flat-conductor power cable would be flared apart and soldered to the ends of the related thin flat-conductor detonator circuit loop that includes the thin conductive foil that is to be explosively vaporized in use, with the attached portion of the assembly permanently sealed between plastic layers. This possible solution is labor intensive, fairly expensive, and since it does not permit the detonator circuit to be detached from the firing circuit during times of system maintenance, potentially quite hazardous. Thus, this second methodology is also not a satisfactory solution to the problem presently under consideration.
The efficiency of air core transformers is not sufficiently high to provide a solution to the instant problem. Additionally, before the advent of the present invention it was commonly believed by those skilled in the relevant arts that the frequency response of ferrite core transformers was too slow for the power pulse transfer of temporally short electric pulses from thick flat-conductor power cables to thin flat-conductor detonator circuits, because such transformers are commonly known to be rated at frequencies no higher than about 400 KHz, while the approximately a few tenths of a microsecond electric power pulse required to vaporize a slapper detonator thin foil has a fundamental frequency of several MHz.